- Don Terry
- Cmdr. Don Winslow
- Walter Sande
- Lt. Red Pennington
- John Litel
- Spencer Merlin
- Wade Boteler
- Mike Splendor
- Samuel S. Hinds
- Adm. Colby - The CINC-US [Ch. 1]
- Claire Dodd
- Mercedes Colby
- Anne Nagel
- Misty Gaye
- Ben Taggart
- John Blake
- Kurt Katch
- The Scorpion
- Herbert Rawlinson
- Adm. Warburton [Ch. 1]
- Dirk Thane
- Lt. Cmdr. Grady [Chs. 1, 12]
- John Holland
- Paul Barsac
- Arthur Loft
- Tranker - Submarine Z-37 Captain [Chs. 1-2]
- Paul Bryar
- Kramer - [Chs. 3-4]
- Ethan Laidlaw
- Spike - Henchman
- Robert Barron
- Prindle - Henchman
- Lane Chandler
- Corley - Henchman
- Peter Leeds
- Chapman - Seaman
- Jerry Mandy
- Tangita Jim [Chs. 2, 10]
- Iron Eyes Cody
- Native Thug at Mill [Ch. 5]
- William Desmond
- Pat - Smelter Foreman [Ch. 5]
- Heenan Elliott
- Captain of the S.S. 'Tarleton' [Chs. 3-4]
- Kenneth Harlan
- Capt. Holding [Ch. 1]
- Edward Hearn
- Mill Henchman [Chs. 5-6]
- Guy Kingsford
- Jackson - Z-40 Submarine Captain [Chs. 7-9-10]
- Frank Lackteen
- Koloka [Chs. 6-7]
- Bert LeBaron
- Radio Room Henchman [Ch. 10]
- John Merton
- Destroyer 620 Helmsman [Chs. 1, 9]
- Irving Mitchell
- Taylor - the Chemist [Chs. 8-9]
- Eddie Polo
- Lab Assistant [Chs. 8-9]
- Jack Rockwell
- Butch Clint - Henchman [Ch. 8]
- Buddy Roosevelt
- Henchman-Helmsman [Ch. 3]
- Paul Scott
- Capt. Fairfield [Chs. 1-2]
- Tom Steele
- Diving Boat Raider [Chs. 10-11]
- Ray Teal
- Parker - Saboteur Radio Operator [Chs. 4-12]
- Ken Terrell
- Sam Munn / Rocky- Henchman (uncredited)
- Dale Van Sickel
- Sailor
- Phil Warren
- S.S. 'Baratavia' Crewman [Ch. 2]
